1. Technical Field
The present invention relates to a bridge conveyor system used in rotary stretch wrapping apparatus that require film engagement guide means to allow the film to travel along in the same direction as the product during wrapping.
2. Description of the Prior Art
Prior art devices of this type have relied on a wide variety of conveyor and guide configurations. Such systems typically use multiple endless belts positioned in stacked relation one above another or single belt systems using side mounted low friction guides. Other air assisted configurations use multiple aperture conveyor surfaces to "float" articles there across. For example, of the hereinbefore described systems, see U.S. Pat. Nos. 4,317,322, 4,979,358, 4,236,851, 4,050,220, 4,711,069 and German Patent DE3431628.
In U.S. Pat. No. 4,317,322 a twin belt conveyor is described that uses the top conveyor belt to hold and transport the product while the second conveyor belt positioned below the first travels in the opposite direction so that the film will engage and travel in the same direction as the product during wrapping.
Applicant's own U.S. Pat. No. 4,979,358 discloses a conveyor system that uses a pair of side by side endless conveyors that use a plurality of expandable supports that travel in one direction supporting the product and engage the film in the return travel direction.
In U.S. Pat. No. 4,236,851 a disk handling system is shown that uses an apertured conveyor surface through which air, under pressure, is supplied "floating" the products thereacross.
U.S. Pat. No. 4,050,220 a simple bundling machine is claimed wherein a conveyor system using conveyor belts mounted on rolls with wrapping guide rails to support the load while it is being wrapped. The rails can also be of a porous or hollow material so air under pressure passes therethrough engaging the film. No claim or drawing is shown illustrating the alleged form of the invention briefly referred to.
In U.S. Pat. No. 4,711,069 a stretch foil wrapping arrangement is disclosed wherein a transition bridge is claimed having upper and lower conveyors including an internal roller plane having an inner portion or an external roller plane having an inner portion or an inner roller plane of the remaining transition conveyor.
In German Patent DE3431628 a device is shown that is directed towards a bridging conveyor for wrapping packages or bundles in stretch foil apparatus wherein a pair of vertical spaced conveyors are used to engage the packages to be wrapped. Foil guides are disclosed on each of the conveyors defined as curved hollow elements that are apertured along their outer curved surface. Compressed air is supplied to the hollow elements defining an air cushion over the guide. The foil defines a sealing area of the guide adjacent its top portion and lower portion in order to trap the air between the two surfaces to form a cushion as required.
The hereinbefore described air cushion systems are not practical in that the apertured hollow supply guides cannot supply air distribution evenly over the guide surface given the economic restrictions of supplying huge quantities of air under high pressure. The key to successful i.e. economical feasibility air cushions is to coat the surface of the support guides with a thin even film of air on which the stretch film under high engagement forces will travel. Applicant's solution to this problem requires precise distribution of the air supply to a high density yet porous material.